Regs for Spiral Stairs vs Kite Winders

[A1Dan]

Asked a few people about this, including building control, who haven't got back to me with a useful answer yet...

The criteria for rise and going set out in Building Regs Doc K effectively give a minimum width of around 860mm for a 3 tread kite-winder (anything less and the centre line going drops below the minimum of 220mm).

However, according to that document, spiral staircases are not subject to the same regulations, but must comply to BS 5395-2 instead. These specifications dictate that for a spiral staircase going to a single loft room (Category A) the minimum total diameter is 1448mm, with a minimum centre going of 145mm.

I'm trying to understand exactly how a spiral staircase (subject to BS 5395-2) is differentiated from a series of winder turns (subject to Building Regs Doc K). The actual geometry of the end result is pretty much the same, so which factors dictate which regulations are in play?

I have plans for a staircase which could be classified as either, depending on the answer to the above!

 

[noseall]

spiral staircase

NOOOOOOoooooooooooooooooooooooooo................

Only Satan himself would be cruel enough to install such a spiteful object in their home. I still bear the mental scars now having worked on a first floor with these evil things installed.

 

[A1Dan]

NOOOOOOoooooooooooooooooooooooooo................

Only Satan himself would be cruel enough to install such a spiteful object in their home. I still bear the mental scars now having worked on a first floor with these evil things installed.

Needs must... Satan probably has a larger house than I do!

I'm hopeful of being able to achieve what I need with reasonably decent-sized winder turns, rather than a traditional narrow & steep spiral staircase. But that's where the original question becomes pertinent... it seems bizarre that we have quite restrictive limits on how small we can make a winder turn, but those limits go out the window if what you make is officially a "spiral staircase" (which as you imply can be so tight and steep as to be pretty lethal!).

Unless I'm missing anything?

 

[A1Dan]

For clarity, what I'm ultimately after is something like the below, which was designed using 3 winder boxes.

Going by Doc K each side of the square needs to be at least around 1700mm to achieve the required going of 223mm.
But BS 5395-2 (Category A – Small Private Stair) only specifies a minimum of 1448mm diameter / 145mm going.

 

[noseall]

Unless I'm missing anything?

Impossible to get large objects upstairs.

 

[A1Dan]

Impossible to get large objects upstairs.

Yes potentially true, but I'm thinking purely in terms of the regs...

 

[freddiemercurystwin]

In layman's terms, as far as I understand it, spiral stairs are only likely to be fitted when space restricts a traditional stair, so the regs are more lenient, just as they are for space-saver stairs. And by their very nature in theory the pitch when measured near the centre is near vertical. Generally the only people using them will be regular users so familiar with their unorthodox manner.

 

[A1Dan]

In layman's terms, as far as I understand it, spiral stairs are only likely to be fitted when space restricts a traditional stair, so the regs are more lenient, just as they are for space-saver stairs. And by their very nature in theory the pitch when measured near the centre is near vertical. Generally the only people using them will be regular users so familiar with their unorthodox manner.

Makes sense in terms of why the rules for spiral stairs are as they are... but still not clear on when they apply.

I've had a joiner tell me that three winder boxes of width 750mm (as per the above diagram) would not meet regs, as the centre going would only be around 196mm.
But if I say it's a spiral staircase (which it essentially is), then it easily meets regs.